1. Field of the Invention
The present invention relates to a wick-based delivery system for transporting liquids, such as fragrances or insecticides, from a reservoir to a surface exposed to the ambient air.
2. Description of the Related Art
Devices that release vapors into the ambient air are well-known in the art. Generally, the purpose of these devices is to deodorize or disinfect the ambient air, or to distribute toxins into the air to kill or repel unwanted pests, such as mosquitoes.
To achieve the goal of dispensing vapors into the air, a number of methods has been employed. For example, aerosol containers have been used to eject vapors into the air upon the activation of a trigger by the user. Other methods, however, have utilized the evaporative properties of liquids, or other vaporizable materials, to cause vapors with desired properties to be distributed into the ambient air. One such evaporative method utilizes a wick to deliver a vaporizable liquid from a reservoir to a surface exposed to the ambient air. As the liquid reaches the exposed surface, the liquid is vaporized and dispersed into the ambient air. The exposed surface may be either the surface of the wick or the surface of another body in fluid communication with the wick.
In some applications, it is desired that the release rate of the vaporizable liquid be greater when the device is first activated. This initial spike effect is particularly desired when the purpose of the device is to release insecticides or insect repellants into the ambient air. In the case of insect repellant, the benefit of the initial spike effect is that it causes the vaporizable liquid (in particular, the active ingredient of the vaporizable liquid) to be quickly dispersed into the air in an amount sufficient to decrease the number of insects in the surrounding area. Once the optimum level of active ingredient has been released by the initial spike and the ambient air of the operating area is sufficiently saturated, however, it is preferable that the release rate of the vaporizable liquid be decreased. This decrease in the release rate is preferred because the optimum saturation level of the ambient air has already been achieved, and the release rate of the vaporizable liquid after the initial period need only be sufficient to maintain that optimum level.
Accordingly, when an insect control device is first activated, it is preferred that the device initially release a relatively high amount of the vaporizable liquid into the ambient air, and then, after that initial spike, the release rate of the device should be maintained at a lower level.
An example of a wick-based, controlled release device is described in U.S. Pat. No. 4,915,301. This patent discloses a bottle for dispensing a liquid in vapor phase. More specifically, the bottle contains a liquid and that liquid is absorbed by a wick and conveyed to a porous body. The liquid then spreads through the porous body and reaches a microporous membrane which permits the liquid to be discharged as a vapor into the atmosphere. The membrane serves to enable emission of vapors of the liquid, while preventing passage of the liquid itself. Accordingly, the exposed surface of this device consists solely of a microporous membrane. Although this membrane helps prevent spillage of the liquid through the wick, it cannot provide an initial spike effect followed by a lower, steady release rate.
U.S. Pat. No. 6,109,539 discloses an inverted aromatic substance dispenser that can be comprised of porous plugs with different porosities. However, this dispenser also has a material of only one pore size exposed to the ambient air and, therefore, this dispenser cannot provide an initial spike effect followed by a lower, steady release rate.
Another wicking device is disclosed in U.S. Pat. No. 2,277,377. This patent discloses a device that comprises a cotton wick surrounded by a sheath made of bentonite, a clay-like substance. The device is inserted into a reservoir to lift liquid from the reservoir to the surface of the bentonite sheath. Again, however, the design of this device is such that material of only one pore size is exposed to the ambient air and, therefore, this dispenser cannot provide an initial spike effect followed by a lower, steady release rate.